This disclosure is directed to a high volume centrifuge system capable of processing great quantities of liquid and removing suspended solids from the liquid. It finds application in food processing industries. It is also useful in waste separation, for example, the waste sludge of a food processing plant. It is also very useful in separating emulsifications into separate phases, i.e., droplets of oil or suspended solids in solution. It also is effective in separating dissolved earth products such as sand, clay, silt, and other particles from water or other liquids. One particular use of significance is the separation of solids formed into an emulsification in drilling fluids that carry drill bit cuttings.
Consider an example of the application of this device. In a drilling rig, the drill bit lubricant is often made of water with suspended clay products in it. This serves as the lubrication system for the drill bit. At the surface, water is mixed with various clay products to form what is known as drilling mud which is pumped down the well borehole through the drill stem, then flows out of the drill bit at the lower end, and is returned to the surface in the annular space on the exterior. It washes away cuttings of the formation. As the cuttings are removed from the vicinity of the drill bit, the well is advanced, the drill bit is cooled and lubricated, and the drilling process continues with recycling of the drilling mud. The drilling mud, however, picks up broken pieces of sand or shale from the formations being penetrated, carries them to the surface where the particles are classified ideally removing the bits and pieces ol the formation so that the drilling mud can be recycled. Recycling involves removing at least some or most of the formation materials from the return mud stream so that it can then be pumped again through the mud pump along the drill stem and back to the drill bit, thereby repeating this cycle. It is not uncommon for the flow rates to be several hundred gallons per minute. Volumes as large as 400 gallons per minute are pumped into the well borehole and returned. With a flow velocity that great, the velocity of the drilling mud in the return annular space is sufficiently fast that the drill bit cuttings are lifted and returned to the surface.
High volume separation is important in the foregoing context. There are devices that are sold for that purpose today. However, they often are limited. There are contradictory design requirements which come into play. These design requirements are manifest in the tradeoffs involved in designing such a high volume device. Consider as an example a high volume centrifuge which has a capacity of about 60 gallons per minute. One such device is the Sharples Model P-95000. This commercially available centrifuge has a pool of about 1,670 sq. inches. The device of the present disclosure can be readily made (in a comparable model) having a pool of about 18,000 sq. inches, or more than about ten times larger. The dwell time of the solids is markedly reduced because the present device has a pool which is about 0.40 inches deep on the average while the above mentioned device has a pool of about 1.8 inches. This represents a reduction of about 75%. By contrast, this device is less than about one-half the length. As length is reduced, the weight of the rotor is reduced. This device is provided with a rotor of 30 inches diameter in comparison with 40 inches; by making these changes, this rotor can have a rotating speed of about 3,000 rpm compared to 2,000 rpm for the referenced device. This reduces the weight of the roller from about 9,000 pounds to about 3,000 pounds. By reducing the weight and shortening the length of the shaft, and yet rotating at a higher velocity, the maximum gravity force is changed from about 2,100 G to the vicinity of 2,800 G at the bottom of the pool and changed from 1620 G to about 3,300 G at the top of the pool in the device of this disclosure. This marked increase in gravity pull with the enlarged pool area results in the representative device of this disclosure having a throughput of something over 400 gallons per minute which is many times greater than the rated throughput of about 60 gallons per minute of the competitive device. The life of the equipment is markedly enhanced. Consider, for instance, the service life of the bearings which are probably the most crucial limit on life. Bearing life is related to the race velocity. If for instance a bearing assembly has the diameter increased by 50%, the race velocity goes up by 50%. Race velocity itself however is limited depending on the design of the race and the bearings in the race.
Therefore the race velocity significantly serves as a limit. As the rotated weight goes up, the size of the bearing assembly must increase to provide a larger number of rotor elements in contact with the raceway to support the greater amount of weight. To be sure, the diameter of the bearing assembly can be reduced by simply doubling up on the number of bearing assemblies. This however is costly in that it makes the equipment longer and requires more bearing assemblies. The optimum way to reduce the cost of the bearing and to increase their life is to reduce the rotated weight which is accomplished in this device. A reduction by two-thirds is significant in extending bearing life.
One advantage of the present apparatus is the incorporation of a disc stack. The disc stack is held in place with a key member aligning the discs. This defines an enhanced surface area. Restated, the disc stack has the advantage of increasing the surface area of the pool. The pool therefore becomes much more expansive. Between adjacent discs, the liquid and sediment suspended in it respond to the increase in gravity. So to speak, a differential between the sediment particles and the liquid of perhaps 1.03 becomes markedly enhanced when exposed to the high gravity forces occurring in the rotating disc. This carries the water to the interior and spins the heavier particles to the exterior. This enables the dry material to be separated more readily and thereby enhances the volumetric throughput.